Cartridges containing medical drugs may be intended for single use or for multiple uses. In the case that the cartridge is intended for single use, only one dose of medical drug is supposed to be dispensed from the cartridge, and any remaining medical drug, exceeding the required dose, is disposed of. Accordingly, the remaining medical drug is wasted. An advantage of single use cartridges is that the cartridge is sealed during filling of the cartridge, and this seal is only broken when the single dose is to be dispensed. Thereby the risk of contamination of the medical drug is minimised, and it is not necessary to add preservatives to the medical drug. However, it is a disadvantage of single use cartridges that the amount of medical drug contained in the cartridge will often not correspond precisely to a required dose, and thereby a substantial waste of medical drug may result, as described above.
On the other hand, in the case that the cartridge is intended for multiple uses, the amount of medical drug contained in the cartridge represents several doses of medical drug. This allows the total amount of medical drug contained in the cartridge to be used to a greater extent than is the case for single use cartridges, even if the required dose varies from one user to another. Accordingly, the waste of medical drug is reduced. However, once the first dose of medical drug has been dispensed from a multiple use cartridge, the sealing of the cartridge has been breached, and there is therefore a risk that the medical drug remaining in the cartridge is contaminated. In order to prevent, e.g., bacterial growth in the remaining medical drug, preservatives are sometimes added to the medical drug. However, the presence of preservatives in the medical drug may be undesirable, e.g. due to possible instability of the medical drug, undesired side effects caused by the preservatives, such as allergic reactions, etc.
In the case that the medical drug is very expensive, it is desirable to minimise the waste of the medical drug as much as possible. However, the presence of preservatives in the medical drug may be unacceptable, and therefore simply using a multiple use cartridge is not an applicable solution.
U.S. Pat. No. 5,478,323 discloses a removable manifold assembly for attachment to the outlet end of a multi-cartridge injection device. The manifold assembly comprises two rigid plastic housings which encapsulate a rubber septum. Check valves are formed by compressing the front surface of the septum against a seal face of the rear housing to form a fluid tight interface therebetween. The check valves prevent that fluid flowing from one cartridge enter one of the other cartridges.
U.S. Pat. No. 5,147,323 discloses a multiple cartridge syringe, including a body housing first and second pharmaceutical-filled cartridges. The cartridges are of the type with a septum at one end and a piston at the other end with liquid pharmaceutical between the two. When the cartridges are mounted within the body, the septums are pierced by hollow spikes which are connected to a flow path opening into an accumulator chamber. Check valves are used at the distal ends of the spikes to prevent liquid flow back into the cartridges.